The failure to stand up to bullies is, of course, an invitation to aggression. And it is worth considering why, in our time, we seem to have forgotten an insight that was old even in fourth-century Athens, known to Plato and Aristotle, but best formulated by the Roman military theorist Vegetius: “Let him who desires peace, prepare for war.” For never in the history of human conflict has so much been owed by those who refuse to defend themselves to those who defend others too. Right now, the United States is the only reason why Russia is not aggrandising itself at the expense of its Baltic neighbours, or China doing the same along the littoral of the South China Sea. Mr Trump has persuaded Congress to approve an increase in annual defence expenditure to more than $700 billion, which is more than three times as much as all the defence budgets of the European Union put together. In security terms, Europe is a free rider.

Such sums, vast as they seem, are of course dwarfed by the costs of a full-scale war, both human and economic. Poland recently demanded that Germany pay $1 trillion in war reparations, a small fraction of the cost of the Second World War. Defence is an insurance premium, and if we accept too many exemptions in order to cut costs, we may find ourselves bankrupt not only financially but morally as well. British defence has been pared down to the point where it is no longer merely making “hard choices” but is left with no choice at all. The finest of our forces — the Royal Marines and the Fleet Air Arm, for example — are losing the capacity to do their jobs: all the navy’s amphibious assault ships are likely to be scrapped and there are no aircraft to operate from the two new carriers now coming into service. It will take until 2024 for a mere 24 of the new F-35B Lightning II planes to come into service on board HMS Queen Elizabeth. No new assault ships are planned. What this steady decline of conventional defence means is that we are more dependent on our American allies than ever before.

The Trump Doctrine is based on national sovereignty. Britain, as an ally, needs to show by our actions that we understand and embrace this principle. The President makes policy in the American national interest. Hence it was unwise of Theresa May to urge him to stick to the Iran deal, which he had concluded was clearly inimical to US and indeed Western interests. Standpoint was one of the few voices warning against the dangers of such a deal. The least the British government should do is to re-examine the evidence on which the President has decided to put Iran on notice that he may renegotiate the deal. The Islamic Republic is now richer and more powerful than ever before. If Iran means us harm, as seems likely, or is at least not to be trusted, as seems certain, Mrs May should have the courage to align herself with Mr Trump. The worst that can happen is that she will be ridiculed. And of all people, our present Prime Minister should not fear to stand the test of ridicule.